Build a wooden SUP split board

[tungsten]

New project! My missus talked me into the most stupid thing I've ever attempted to build. She wants a SUP, which is fine. She wants a wooden SUP, which is also fine. She wants it to be light, which is quite understandable. She wants it to be as compact as it gets for her, which I appreciate. And she wants it to be a SPLIT BOARD to fit in the car with ease.

This board has not one right angle into it. Madness. Here's a first glimpse. I'll do the full write up when it's finished.

Cheers and good winds,

tungsten

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[Lonny]

You are awesome... I hope the missus knows how talented you are. My wife would have gotten an inflatable...

[spewing]

I really like watching your projects.

Looking forward to seeing this one progress.

[yotiro]

You're really inspiring with your build projects.
Thanks for sharing all that information with us.

Did you finish and tested this SUP board?

Cheers
Fernando

[tungsten]

So there we go. I finally finished the board a couple weeks ago. It was a lot more work than I thought, because I had to try lots of things I haven't done before. The split construction was new to me. So I studied glider wing construction, catamarans and a couple other constructions where light, strong and flexible is the call. I did some basic calculations to get an idea of the longitudinal forces I'm dealing with in the waves, and tripled the results to get a sturdy board. The construction looks fragile but is incredibly strong: the wooden construction in Paulownia is strong enough for the purpose. I added 2 layers of 4OZ E glass on top and bottom, with wrapped rails, to make a really strong board.

As the board is hollow, I had to insert a plug in either section to make sure it's not being damaged with changing temperatures. Left in the car, the board heats up easily to 80+º C in summer. That is a 60 to 70ºC difference to storing and to water temperature. 60ºC rise is equal a 25% pressure rise. That's enough to explode any board - 2.5N per square cm (0.25 bar or 3.6 psi) is a lot of internal pressure. I actually didn't like the pressure plugs on sale, because I believe 25 bucks for a plastic cap is an insult, be it IP 68 or not, and on top they are fugly. 2 plugs at 25 bucks each would have consumed half of my budget for this board . So I made my own ones out of standard half inch brass water pipe material and a piece of gore tex cloth which I cut out of the inner pocket of an old sailing jacket. Again I had to test this stuff for water tightness, flux rate and so forth. Many working hours went into this kind of tinkering. But it was good fun to MacGuiver my own board. It's a hobby after all.

The fin is an old windsurf fin, a friend left me a couple fins he's not using anymore because he gave up on pole dancing.

My design is the attempt to make a compact yet stable board: the outline is taken from a starboard shape which gets good critics. the rocker however is a lot flatter along the center line making for a fast board, and I used a deep concave to achieve a much more pronounced rocker line along the outline of the board in order to have a good maneuverability in waves. On top, flat deck and deep concave give me a volume distribution with lots of volume in the rails. This makes for a laterally stable board, just like a catamaran, where all the volume is located at the outermost point on either side. My missus is a SUP rookie, and after all the board is for her.

Construction is as always simple: the inner frame is 5mm light ply wood; the rest is paulownia, cut into 2cm x 5mm strips for the deck and bottom, and to fit for the carrying inner construction of the split section. Simple does not mean easy though. As the board has rocker and deep concave, I had to build a rather complex 3D body with a very small error margin. Lots of measuring + cutting to size, which took extra hours' toll.

t.b.c.

[tungsten]

The design and measurements:

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Board weight came out at 12.5 kg ready to ride, which I'm happy with. If I would have worked it not as a split board but in one piece, It'd be around 10,0 kg.

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t.b.c.

[tungsten]

The basic construction was carried out on a frame. In order to make sure everything is in its place, I used a 3m x 10cm x 10cm pine wood bar and mounted the ribs and stringer with screws onto that:

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Then I started building the deck, gluing strip by strip on top.

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t.b.c.

[tungsten]

When the upper deck was ready, I turned th board around and started building the reinforcements for the split construction.

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[tungsten]

With the basic construction in place, I cut the board in half.

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t.b.c

[tungsten]

Getting to build the bottom and outline:

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Now that starts to look more like it. When you look closely, you see the space for the fin box is carved out already.


t.b.c.

[tungsten]

I will spare you the gluing of side walls and bottom. One by one, from the middle (stringer) to the outside (rail), in pairs to avoid uneven tension, they are glued on with gorilla glue (class D4 water resistant polyurethane wood glue).

I'm always using this glue for wood, because it's easy to sand. Using epoxy for gluing wood is plenty strong, but difficult to sand: soft wood and hard epoxy glue in between is not going to make an even surface by sanding. So. Gorilla glue is the way.

Here's what it looked like closed and evened out with the fad. Grip holes are made already, as well as the holes for the leash plug and the pressure plugs. It becomes obvious why proper calculation was necessary: the split is angled. So I had to take the thickness of the construction, including the lay up, into consideration. Otherwise the bottom of the board would not be even, it would have a step in it. I am quite pleased with the result.

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And a closeup on the junction:

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t.b.cont'd

[tungsten]

Glassing and mounting the pressure plug:

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The pressure plug is dead simple: I drilled 3 holes in the end cap. The pipe connector is epoxie'd into the board. The rubber sealing is glued onto the gore tex fabric, cut out and inserted into the end cap. That's all there is to it.

[tungsten]

Almost there.

The 2 parts of the board are held together with 6 bolts and a capped allen screw on either side. Those bolts are running in alloy tubes through the board. I chose to glue in alloy tubes for 2 reasons: first of all they guarantee the exact position of the bolts, and second of all they are not compressed by the bolts, as opposed to running the bolt through a hole drilled through the wood and left without reinforcement.

The deck pad is as usual EVA floor mats ground down to 6mm and glued on with epoxy or contact cement.

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[tungsten]

The paddle is also home grown, made of one piece of 2cm paulownia with bits glued on top and bottom for reinforcement. In order to achieve the 10 degree angle, I bent the pre cut shape over vapor. 2 layers of 4 OZ and epoxi got everything in good shape. The paddle is really nice, weighs 600grams (19.5 OZ), is super sturdy and has a very nice flex to it. Sturdy means, I tried to break it leaning my 90kg on it and couldn't. That should be plenty strong enough for the missus' feather weight.

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That's it so far, I will be testing the board in the next couple of days and take some better pics of the board in action. Hope you enjoyed!

There's many construction details I didn't explain exhaustively. Any old question, fire away.

cheers, tungsten

[tungsten]

First beach day with the missus, kids and board! The kids had an absolute ball, which I expected (new toy) but was nice to see nevertheless. The missus is grinning all over her face, because the board works amazingly well for her. The little trick with the flat rocker along the center line, deep concave and lots of volume in the rails makes for a very stable board which gets going with ease. I am positively surprised how well it works - figuring something out on paper and seeing it work (or not) in real life is two different things. This thing is seriously fast.

To be honest, I picked the basic idea from an article I read about water taxis in Venice: boats with the usual hull shape do a lot of damage to the channels with the waves produced in their wake, washing onto the walls and eroding the bricks. A couple of years ago, Venice authorities introduced a catamaran kind of water taxi which does not produce any wake - the outline is straight, the wake is produced between the catamaran hulls in the middle of the boat, and thus eliminated by the opposite hull - all comes down to choosing the right longitudinal shape. And if there's no wake, you don't spoil energy to create one, which means an effective shape.

The shape is a huge success. With its 140 odd liters, the board even works well with my 90kg. It feels more laterally stable and gets going faster than lots of 230+ liter boards I rode. I am amazed. I hope some SUP shapers will give this idea a shot, as the result is a small board that feel stable like a big one, but turns like a small one. Thanks to Starboard for borrowing me the outline, they seem to know their biz.

Speaking of theory vs. real life: towards the end of our beach day, I snapped the paddle clearly in half. Yes, the one I could not break when I tried to. I was kneeling on the board and powering in, because my daughter was holding the board by the leash and I tried to escape her. Bang! and giggles.

This pissed the missus off a wee bit, but I assured her I'd fix it in no time. So. Conclusion: a slightly different hand position while kneeling showed that the layup was too weak and should not be evenly distributed over the length of the shaft - it's got to be tapered from where the hand is positioned (in the middle of the shaft) towards grip and blade. Pretty much like a long bow, thick in the middle, thin at the extremes. Another lesson learned.

cheers, tungsten